>>1. Granite units need something flexible in the outer
20-50mm of the joint, because the skin of the granite
will expand more than the core due to thermal movement
of the surface.  If there are any hard contact points
in the outer portion of the joint, the outcome is
likely to be shell-shaped spalls off the face of the
granite.<<

Is this why I sometimes see a fold of lead in outer edges of the joints of
granite foundation stones here in northern New England?

John Leeke

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